Public law

Lore & Background

The distinction between public law and private law dates back to Roman law, where the Roman jurist Ulpian first noted it. Ulpian argued in the Institutes that 'public law is that which respects the establishment of the Roman commonwealth, private that which respects individuals' interests.' Roman Law conceived of the law as a series of relationships between persons and persons, persons and things, and persons and the State, with public law consisting of the latter. However, Roman lawyers devoted little attention to this area, focusing largely on private law. The distinction was of great importance in later legal history, but contrary to some claims, Roman law—not Teutonic society—is widely recognized as the origin of the public-private divide. Drawing a line between public and private law largely fell out of favor in the ensuing millennium, though medieval jurists saw a concern with the Roman conception of the res publica inherent in the legal fiction of the king's two bodies. Legal philosophers during this period were largely theologians operating within Canon Law, concerned with distinctions between divine law, natural law, and human law. The public/private divide returned in the 17th and 18th centuries through the emergence of the nation-state and new theories of sovereignty. Claims by monarchs and parliaments to unrestrained power spurred attempts to establish a distinctly private sphere free from encroaching State power. For many years, public law occupied a marginal position in continental European law, with private law considered general law and public law consisting of exceptions. It was not until the second half of the twentieth century that public law began to play a prominent role through the constitutionalization of private law and the development of administrative law and various functional fields. In Italy, the development of public law was considered a project of state-building, following the ideas of Vittorio Emanuele Orlando.

Reader's Guide

Public law is significant because it establishes the legal framework for the relationship between the state and individuals, ensuring that government authority is exercised within the bounds of law. The distinction between public and private law, first articulated by Ulpian, has shaped legal systems in both civil-law and common-law traditions. Public law includes constitutional law, which lays out the foundations of the state and the rule of law; administrative law, which regulates bureaucratic procedures and defines powers of agencies; criminal law, which relates to crime and punishment; and tax law, which concerns the relationship between persons and the state regarding taxation. The borderline between public and private law is not always clear, and the distinction is largely functional rather than factual. The theoretical understanding of public law has been extensively discussed in German-language legal literature, with theories such as the interest theory emerging from Ulpian's work and elaborated by Montesquieu. Public law's legacy includes its role in elevating legal protections and acknowledging that few areas of law are free from potential state intervention.

Did You Know?

• The distinction between public and private law was first made by Roman jurist Ulpian.
• Public law comprises constitutional law, administrative law, tax law, criminal law, and some procedural law.
• The borderline between public and private law is not always clear and is largely functional rather than factual.
• Tax law has been part of public law since ancient times, for example in Roman law.

Definition and Scope of Public Law

Public law constitutes the branch of legal regulation that governs the interactions between legal persons and government, between different institutions within a state, between branches of government, and between individuals in matters of direct societal concern. Its constituent fields span constitutional law, administrative law, tax law, criminal law, and all procedural law. This stands in contrast to private law, which addresses relationships among individuals. Importantly, the boundary between the two categories is not always sharp. Law as a whole cannot be neatly partitioned into 'law for the State' and 'law for everyone else.' The distinction is therefore largely functional rather than factual, classifying legal rules according to which domain the activities, participants, and principal concerns involved best fit into. This functional character has prompted scholars to seek a deeper theoretical foundation for what constitutes public law. A practical illustration: an individual who enters into a service contract with the government would typically fall within private law, even though the State is a party to the arrangement.

Ancient and Medieval Roots

The intellectual lineage of public law begins with the Roman jurist Ulpian (c. 170–228), whose passage in the Institutes—preserved by Justinian in the Digest—declared that public law respects the establishment of the Roman commonwealth, while private law respects individual interests. Ulpian further characterized public law as covering religious affairs, the priesthood, and state offices. Roman legal thought organized law into relationships among persons, between persons and things, and between persons and the State, with public law occupying the last category. Yet Roman lawyers devoted comparatively little scholarly attention to this area, concentrating instead on private law. German legal historian Otto von Gierke later identified Teutonic society as the true 'fathers of public law,' where it held far greater practical importance. For roughly a millennium, the public-private divide largely receded from legal scholarship. Medieval jurists, operating within Canon Law, were preoccupied with distinguishing divine, natural, and human law. The divide re-emerged in the 17th and 18th centuries, as the rise of the nation-state and new sovereignty theories crystallized notions of a distinctly public realm.

Governmental Accountability and the Rule of Law

A defining feature of public law is that it governs relationships that are inherently asymmetric and unequalized. Government bodies, whether central or local, possess the authority to make binding decisions about the rights of persons. However, this power is not absolute. Under the rule-of-law doctrine, authorities may act only within the law—expressed in the Latin principle secundum et intra legem. The government itself must obey the law it enforces. This principle creates a critical check: a citizen who is dissatisfied with a decision rendered by an administrative authority can petition a court for judicial review, thereby subjecting governmental action to independent legal scrutiny. Constitutional law, as the foundational layer of public law, postulates the supremacy of law in the state's functioning, sets out the form of government including the division of powers among the executive, legislature, and judiciary, and establishes the fundamental human rights that must be protected for every person. Together, these elements define the borders of what any government must and must not do, ensuring that state power remains bounded by legal constraint.

Public Law Across Legal Traditions and Its Modern Rise

Although the public-private divide is most commonly discussed within Continental European civil-law systems, it is not exclusive to them. Common-law jurisdictions, including England and Canada, acknowledge the distinction even if unconsciously, recognizing that actions the State must prohibit need not necessarily be prohibited for private parties as well. For many years, public law occupied a marginal position in continental European legal thought, with private law regarded as the general law and public law treated as a collection of exceptions. This changed dramatically in the second half of the twentieth century. The constitutionalization of private law, the growth of administrative law, and the emergence of functional fields such as labor law, medical law, and consumer law elevated public law from its once-marginal status. In Italy, the development of public law was explicitly framed as a project of state-building, following the ideas of Vittorio Emanuele Orlando, and many early Italian public lawyers were also active politicians. In France today, public law encompasses constitutional law, administrative law, and criminal law, reflecting its central role in modern governance.

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